A newborn has aniridia and normal DNA sequencing of the PAX6 gene. What is likely causing her symptoms?

The presence of aniridia, or absence of the iris, alongside normal sequencing of the PAX6 gene suggests that the mutations responsible for the condition are not located within the coding regions of the gene itself. Instead, disruptions in regulatory sequences could lead to improper expression of the PAX6 gene, which is crucial for eye development.

Regulatory sequences play significant roles in controlling the timing, location, and level of gene expression. If there is a mutation in these regulatory elements, PAX6 might not be expressed adequately or at the right time during development, resulting in the observed symptoms of aniridia despite the gene's coding region being intact. This highlights the importance of these non-coding regions in gene regulation and development.

In contrast, mutations such as point mutations in exons or the creation of new stop codons would typically affect the protein that is synthesized directly from the coding region and likely would have been detected during DNA sequencing of the gene. Similarly, a deletion of an intron pertains to the protein-coding elements as well, and such alterations would generally be visible in the gene sequencing results, leading us to the conclusion that the source of the symptoms lies in the regulatory mechanisms associated with the gene, not within the coding sequence itself.